This invention relates to projection display systems, and more particularly to SLM-based projection display systems that are portable and minimal in size.
Current projection display systems are made with a variety of different image generating devices. One type of image generating device suitable for projection display systems is a spatial light modulator (SLM). SLM""s are arrays of pixel elements, each of which is individually addressable with image data. An image is generated by addressing all pixel elements at once, such that each is on or off. Various modulation schemes may be used to provide greyscale. SLMs include both reflective and transmissive devices.
A DMD(trademark) is a type of reflective SLM, having an array of tiny mirrors. Each mirror can be tilted to an on position or an off position. Each image is generated by switching the appropriate mirrors on or off and by modulating the time that the on mirrors are on. Images can be generated in such a fast sequence that the viewer perceives motion.
Color may be added to the images by filtering the source illumination through a motorized color filter wheel. The color filter wheel spins in sequence with the images"" corresponding red, green, or blue data. Mirrors are turned on or off depending on how much of each color is needed per pixel. As an alternative to, or in addition to, a color filter wheel, multiple DMDs can be used. The projection system has an optical path that comprises the source of illumination, illumination optical elements, the color filter wheel, the DMD, a projection lens, and other optical elements.
Each DMD mirror element has a square surface area. Each DMD mirror element rotates about a hinge axis that is along the diagonal of the square, rather than along a cartesian axis parallel to the pixel sides. As a result, the light that illuminates the mirror elements must be incident to the mirror elements about an axis essentially orthogonal to this 45 degree diagonal in order to exit the mirror in the proper direction for projection. For display, in order to provide correctly oriented images, the SLM must be oriented with the pixel array squarely aligned to the display screen, therefore the architecture of the illumination system must include folds in the optical path. This is accomplished with mirrors and other optical devices that redirect the optical path. These folds tend to dictate the size of the optical unit, and therefore the size of the projector. They also tend to create areas of wasted space within the projector housing.
One aspect of the invention is an SLM (spatial light modulator)-based projection display system. The display system is contained in a two-part housing, one part being an articulating unit and the other being a stationary platform. Articulation is achieved by rotation, translation, or a combination of rotation and translation relative to the stationary base. The articulating unit contains at least some or all of the optical components of the display system, including the SLM. The articulating unit is moveable from a stow position to an operating position at an angle or displacement relative to the stow position. The articulating unit is placed in the operating position during use of the display system, which causes images formed by the SLM to be oriented at a position suitable for viewing. The platform unit rests on a flat surface when the projection display system is in use and supports the articulating unit. A joint mechanism, such as a hinge, attaches the articulating unit to the platform unit, and some sort of locking mechanism holds the articulating unit in place when the articulating unit is in the operating position.
An advantage of the invention is that it permits the form factor for SLM-based projectors to be minimized, particularly in the height dimension, when in the stow condition. The projector can be stowed to a minimal form factor when not in use, but opened up to the correct optical path when in use. In the stow position, the optical path can be packaged within parallel planes less than two inches apart. Because the optical path has previously driven the projector height, the entire projector can now be much slimmer and smaller overall, facilitating portability. The two inch height (or less) now made possible is much smaller than the four inch height or so required for previous designs having xe2x80x9cstationaryxe2x80x9d optical paths.
Most of the embodiments described herein also eliminate the use of a fold mirror to re-orient the image or facilitate packaging. This in turn eliminates degradation of optical efficiency and lengthening of the overall optic path that would otherwise be caused by the fold mirror.